The present invention relates to electrical heating of soils, particularly to powerline-frequency electrical heating of soils, and more particularly to electrical heating of soils using high efficiency electrode patterns and power phasing wherein only one phase of a power system is connected to the current injection or heating electrodes.
Powerline-frequency (60 Hz) electrical heating of the area surrounding a wellbore and between wellbores has been used for several years in the oil industry to enhance the extraction of heavy oils. Powerline-frequency heating is more cost effective than radio-frequency heating due to the use of conventional equipment. More recently, efforts have been carried out to use electrical heating in conjunction with vacuum extraction as a means of removing volatile organic compounds from the soil. Methods for improving the uniformity of the soil heating distribution have been proposed and can be shown to improve the uniformity, but have the following drawbacks: 1) they involve the design and construction of very specialized and expensive hardware, and 2) they are not efficient and are therefore not cost-effective. Thus, a need exists for a simple, cost-effective and efficient way of uniformly heating the soil by current injection.
This need is satisfied by the present invention which utilizes an arrangement which consists of several heating electrodes around the periphery of a volume of soil to be heated--all connected to one phase of a multi-phase or single-phase power system, and a return electrode or electrodes located inside the volume to be heated connected to the remaining phases (multi-phase) or the neutral side of the power source (single-phase). By this arrangement, the size and shape of the volume of soil to be heated is arbitrary, any number of electrodes can be used on the periphery of the volume, and may be located vertically or horizontally in drilled holes or trenches.